How can i edit value in Measure tool 2.8
Press N to bring up a side panel. With a target edge/vertex selected, go to Item and adjust the position of it using the fields shown below. Press and hold LMB to use slider, single press to enter a value. Note that you can enter math expressions, so entries such as -1 + 52 / 2  or  10m - 5cm are completely valid.



Edit:

The amount you want to change the length by will be the amount you will need to change the location in the corresponding axes. In this case, I've extended the length of the rectangle below by 2.75 ft by moving the Y-axis position of the edge by 2.75 ft

Depending on the orientation of your object, you may need to add or subtract to the value for the X, Y or Z axis.